1. Field of the Invention
The present invention relates to an organic light-emitting device and a display apparatus including the organic light-emitting device.
2. Description of the Related Art
An application example of an organic light-emitting device is an organic EL display. The realization of an organic EL display having excellent performance such as low power consumption, high luminance, and a long life requires further improvement in performance of a material for the display. Moreover, in order to realize a low-cost organic EL display, production of an organic EL display by a coating process using, for example, a high molecular weight (or polymeric) material is now mainstream.
One of the problems encountered when using the high molecular weight material is that a high molecular weight organic light-emitting device has a shorter operating life than that of a low molecular weight organic light-emitting device. In general, a high molecular weight material is synthesized by polymerizing at least one kind of monomers. However, the resulting high molecular weight material has a molecular weight distribution and is extremely difficult to be purified, which is a main factor that adversely affects the device operating life.
In addition, there is also the problem that the flatness and electronic characteristics of a thin film formed of a high molecular weight material largely vary depending on the forming method or processing conditions thereof.
To overcome the above-mentioned problems of the high molecular weight material, attempts have been made to improve the device operating life by using a dendrimer having an intermediate molecular weight (Japanese Patent Application Laid-Open No. 2003-231692).
The conduction of a thin film formed of organic molecules is described by the hopping conduction of charges or electrons. In general, in the organic compound, there is a tendency that those having high planarity of molecular structure and large overlap of Π electrons provide high mobility, even in the form of an amorphous film. The tendency can also be presumed by the fact that pentacene, porphyrin, or the like shows high mobility in an organic thin-film transistor (organic TFT).
In this regard, Π-Π stacking fluorene compounds have been reported as compounds having an intermediate molecular weight (“J. Am. Chem. Soc.”, 125, 15474 (2003)). In those compounds, the emission of light from fluorene excimers by photoexcitation has been observed. In general, it is meant that a molecule causing such excimer emission has a large interaction between chromophores in the same molecule, that is, has a large overlap between the orbitals of the chromophores. Therefore, such Π-Π stacking molecules are expected to have high mobility of charges or electrons upon hopping conduction of the charges or electrons owing to the effect of large overlap between orbitals of molecules.